The present invention relates to turbine buckets of steam turbines and, more particularly, to sealing of steam turbine bucket hook leakages using a braided rope seal.
Within a steam turbine, buckets (airfoil, platform and dovetail) turn the flow while extracting energy from steam. In a reaction-style turbine design, these individual buckets are slid into a circumferential groove around the turbine rotor. There exists a leakage circuit around the bucket aft (downstream) hook to the rotor axial load surface. This leakage bypasses the bucket, and therefore the energy is not extracted from the steam. This over-the-hook leakage in this area may be significant due to the assembly issues and bucket loading issues that could cause the bucket to lift off of this axial load surface that is being sealed.
In an exemplary embodiment of the invention, a steam turbine includes a rotor supporting a plurality of turbine buckets. The rotor has shaped grooves for receiving a complementary-shaped bucket hook formed on an end of each of the turbine buckets. A rope seal is disposed in each interface between the bucket hooks and the shaped grooves, respectively.
In another exemplary embodiment of the invention, a method of constructing a steam turbine is provided, where the steam turbine includes a plurality of buckets with bucket hooks and a rotor with grooves shaped corresponding to the bucket hooks. The method comprises the steps of inserting a rope seal in each of the rotor grooves; and securing the buckets in the rotor grooves, respectively, via the bucket hooks, whereby the rope seal is disposed in each interface between the bucket hooks and the grooves.
In still another exemplary embodiment of the invention, a rotor assembly for a steam turbine includes a plurality of shaped grooves for receiving a corresponding plurality of turbine buckets via complementary-shaped bucket hooks formed on an end of each of the turbine buckets. The rope seal is disposed in each interface between the bucket hooks and the shaped grooves, respectively.